1. Field of the Invention
The subject invention generally relates to a sensing device for determining a rain rate on a surface. More specifically, the subject invention relates to a sensing device for determining the rain rate of raindrops striking a glazing (i.e. windshield, rear window, side windows, etc.) of a vehicle such that a wiper is activated to remove the raindrops from the glazing.
2. Description of the Related Art
Various sensing devices for detecting raindrops are known in the prior art. One example of such a device is disclosed in U.S. Pat. No. 5,119,002. Specifically, the '002 patent discloses a device which includes a piezoelectric vibration sensor, an amplifier, a processor, a motor, a wiper blade, and a windshield. The piezoelectric vibration sensor and the amplifier are disposed within a raindrop detector. The raindrop detector is placed on the hood of a vehicle. When raindrops strike the raindrop detector, vibrations are produced. The piezoelectric vibration sensor generates a signal corresponding to these raindrops. The amplifier increases an amplitude of the signal. The processor calculates an intermittent period based on the intensity of the signal and uses that intermittent period to operate the motor. The motor in turn moves the wiper blade.
The '002 patent does not disclose an analog-to-digital converter (ADC) to convert the analog signal into digital values. An ADC allows a processor to perform high-order algorithmic calculations on the digital values that represent the analog signal. Without the digital values, it is very difficult to determine the actual rain rate. In addition, the signal provided to the microprocessor will contain noise from non-rain vibrations, such as wind, engine vibrations, etc. The microprocessor of the '002 patent mistakenly utilizes the noise in calculating the intermittent period, leading to improper actuation of the wiper blade.
Another example of a sensing device of the prior art is disclosed in U.S. Pat. No. 5,059,877. The '877 patent discloses a sensor block mounted on a windshield. The sensor block includes an array of light emitting diodes (LEDs) and an array of phototransistors. A control system that is associated with the sensor block includes an amplifier and a microcontroller. The microcontroller includes an ADC and a processor to determine the rain rate of rain striking the windshield. The '877 patent does not disclose the use of a piezoelectric vibration sensor to generate a signal when raindrops strike the windshield. A piezoelectric vibration sensor can detect vibrations anywhere on the windshield, not just in the limited area that is illuminated by the LEDs of the '877 patent.
Due to the deficiencies in the sensing devices of the prior art, there remains an opportunity to introduce a sensing device that is capable of calculating the rain rate using an equation derived from a point process equation. Very little filtering or signal conditioning of non-rainfall vibrations is needed to very accurately determine the rain rate in this fashion.